Github: revise branch validation regex
Github: revise branch validation regex

The validation now follows the rules defined in git check-ref-format
man page [1]

Issue #193

[1] http://www.kernel.org/pub/software/scm/git/docs/git-check-ref-format.html

mantisbt-plugins/source-integration,mantisbt-plugins/source-integration,mantisbt-plugins/source-integration,make-all/source-integration,dregad/source-integration,dregad/source-integration,make-all/source-integration,dregad/source-integration,make-all/source-integration